Limiting the pressure losses of a heating network is one of the technical features that can improve overall performance. A few weeks ago, we explained why and how heat loss must be combatted: loss of heat and power – i.e. the calories lost – for the movement of water within a district heating network. Today, we are looking at another important criterion for energy performance: pressure losses.
What is a pressure loss in a heating network?
Pressure losses denote the drop in pressure which occurs when water travels through pipes. This phenomenon is valid for water, but also for all fluids in the liquid state. The higher the viscosity of a fluid, the more significant the pressure losses are.
When fluid flows in a pipe, it adheres more or less to the wall, which slows down its flow. This viscosity is called the fluid’s resistance to flow. For example, water is more fluid than oil (due to its fatty and viscous texture) and therefore adheres less to the walls of a tube. Each fluid has its own kinematic and dynamic viscosity, which varies with temperature. Generally, the hotter the fluid is, the more its viscosity decreases.
There are two types of pressure losses:
– Regular pressure loss: characterized by the adhesion of water to the inner wall of the tube, and which applies to straight portions of the heating network.
– Singular pressure losses: in this case the water adheres to the inner wall of the tube in passages such as bends, tees, valves, reductions, purges.
Singular pressure losses are occasional. Thus, if the specific points are few, losses tend to be neglected. Conversely, we always take into account regular pressure losses – which are always important.
Calculating and minimising pressure losses in a heating network
For all heating network, the engineering consultants are responsible for calculating the losses. This phenomenon is expressed as a unit of pressure, either in bars or Pascals (Pa – SI unit of pressure).
It is essential to calculate the pressure loss of a heat network to determine the power of the pump of the substation which will allow the water to be constantly moving and flowing in the network at the desired speed. The calculation of pressure loss also can guide the selection of the diameters of each section of the network according to the power sub-stations. The use of smooth pipes limits friction and hence the losses, especially regular pressure losses.
Image source: Flickr (PAN ANT)
